The present invention generally relates to lift structures and/or load-bearing vehicles.
Historically, there have been developed a wide range of lift structures that are arranged in such a manner as to elevate personnel or material in order to provide facilitated access to an elevated location.
Different types of lifts vary in size, shape and function. For example, xe2x80x9cvertical polexe2x80x9d lifts generally involve the use of a telescoping mast or sequentially extending mast (in which mast segments are usually xe2x80x9cstackedxe2x80x9d along a horizontal direction and then propagate upwardly one-by-one), on which is mounted a basket, cage or other platform structure intended to carry one or more individuals. Most xe2x80x9cvertical polexe2x80x9d lifts are intended to carry only one individual, however, and are generally designed to elevate solely in a vertical direction. U.S. Pat. No. 3,752,261 (Bushnell, Jr.), U.S. Pat. No. 4,657,112 (Ream et al.) and U.S. Pat. No. 4,015,686 (Bushnell, Jr.) disclose general examples of such lifts.
xe2x80x9cScissors liftsxe2x80x9d, on the other hand, involve the use of a scissors-type mechanism for propagating a basket, cage or platform upwardly. Again, the propagation is solely along a generally vertical direction, but in this case the more rigid structure of the scissors mechanism permits greater loads to be propagated and carried. U.S. Pat. No. 5,390,760 (Murphy) and U.S. Pat. No. 3,817,846 (Wehmeyer) disclose general examples of such lifts.
xe2x80x9cBoom liftsxe2x80x9d involve the use of a pivotable, and often extendible, boom structure to propagate a basket, cage or platform both upwardly and in a variety of other directions. U.S. Pat. No. 3,861,498 (Grove) and U.S. Pat. No. Re. 31,400 (Rallis, et al.) disclose general examples of such lifts.
Other types of lifts, not typically falling into one of the three categories outlined above, can also be used for similar purposes, that is, for propagating personnel or material in a generally upward direction to access an elevated workspace. U.S. Pat. No. 4,488,326 (Cherry), U.S. Pat. No. 3,927,732 (Ooka et al.), U.S. Pat. No. 5,299,653 (Nebel), U.S. Pat. No. 4,154,318 (Malleone), U.S. Pat. No. 4,799,848 (Buckley) and U.S. Pat. No. 4,147,263 (Frederick et al.) disclose general examples of lifts outside of the three categories discussed above.
Many types of vehicles and lift structures, especially boom lifts, excavators, cranes, backhoes, and certain other machines, have centers of mass that migrate significantly during use. In contrast, automobiles and similar vehicles have their lateral centers of mass located at some point substantially along the longitudinal axes thereof and these tend not to migrate significantly at all. Thus, a migrating center of mass has been a perennial problem with certain vehicles or machines, including boom lifts.
For example, as the boom of a boom lift is extended and a load is applied to the platform or bucket thereof, the lift""s center of mass moves outwardly toward the supporting wheels, tracks or outriggers. If a sufficient load is applied to the boom, the center of mass will move beyond the wheels and the lift will tip over. The imaginary line along a support surface (e.g., the ground) about which a vehicle tips is known as the xe2x80x9ctiplinexe2x80x9d. A more detailed discussion of the principles of tipping is provided in copending and commonly assigned U.S. patent application Ser. No. 08/890,863, which is hereby incorporated by reference as if set forth in its entirety herein.
By defining the tipline of a vehicle as near to the perimeter of the vehicle""s chassis as possible, the stability of the vehicle is increased. This increase in stability permits the vehicle to perform its intended function with the minimum amount of necessary counterbalance weight, which results in lower costs, improved flotation on soft surfaces, easier transport, etc.
In the context of boom lifts, two types of stability are generally addressed, namely xe2x80x9cforwardxe2x80x9d and xe2x80x9cbackwardxe2x80x9d stability. xe2x80x9cForwardxe2x80x9d stability refers to that type of stability addressed when a boom of a boom lift is positioned in a maximally forward position. In most cases, this will result in the boom being substantially horizontal. On the other hand, xe2x80x9cbackwardxe2x80x9d stability refers to that type of stability addressed when a boom of a boom lift is positioned in a maximally backward position (at least in terms of the lift angle). In most cases, this will result in the boom being close to vertical, if not completely so.
In a typical boom lift, not only can the boom be displaced (i.e., pivoted) through a vertical plane, but also through a horizontal plane. The horizontal positioning is usually effected via a turntable that supports the boom. As the wheeled chassis found in typical boom lift arrangements will usually not exhibit complete circumferential symmetry of mass, it will be appreciated that there exist certain circumferential positions of the boom that are more likely to lend themselves to potential instability than others. Thus, in the case of a boom lift in which the chassis or other main frame does not exhibit symmetry of mass with regard to all possible circumferential positions of the boom, then a greater potential for instability will exist, for example, along a lateral direction of the chassis or main frame, that is, in a direction that is orthogonal to the longitudinal lie of the chassis or main frame (assuming that the xe2x80x9clongitudinalxe2x80x9d dimension of the chassis or main frame is defined as being longer than the xe2x80x9clateralxe2x80x9d dimension of the chassis or main frame). Thus, when designing the boom lift for safety requirements, these circumferential positions of maximum potential instability must be taken into account.
Historically, it has been the norm to ensure the presence of a counterweight to the boom. In this manner, when the boom is in a maximally forward position, the counterweight, situated on the opposite side of the tipline from the boom, will help counteract the destabilizing moment contributed to by the boom (with personnel or material load).
The use of a counterweight does have somewhat of an opposite consequence, however, when one considers the issue of backward instability. Particularly, when a boom is moved into a maximally backward position, it will be appreciated that a destabilizing moment, contributed to by the boom (with personnel or material load) and counterweight, could act in a backward direction. On the other hand, if a destabilizing moment is not present, even a small net stabilizing moment might be undesirable. Thus, it has been the norm to accord the chassis or other main frame an even greater weight than might be desired, for the purpose of counterbalancing the destabilizing moment that contributes to backward instability.
Although the measures described hereinabove have conventionally been sufficient to reduce the risk of vehicle tipping in either a forward or a backward direction, concern has arisen in the industry over the costs associated with providing an overly massive vehicle chassis. The mass of a vehicle chassis not only has ramifications in manufacturing costs, but also in transport costs or in other factors, such as the load that might be applied to fragile surfaces (e.g. mud). Accordingly, a need has been recognized in conjunction with keeping such additional mass to a minimum.
Therefore, a need has been recognized in conjunction with the provision of a lift structure of reduced weight that does not compromise stability and/or with the provision of a lift structure in which a greater range of movement of the item being moved is provided for a given overall weight of the lift structure.
Other needs have been recognized in conjunction with given lift structures, as discussed herebelow.
An important consideration in the design and manufacture of load-bearing apparatus, such as boom lifts, is the range of motion afforded by the apparatus or lift. Typically, a lift or other type of load-bearing apparatus will have a predetermined xe2x80x9cwork envelopexe2x80x9d based on the components used in manufacturing the apparatus as well as the geometry, positioning and dimensions of such components. Depending on the intended use of the apparatus at hand, it might be desirable to provide a significantly large work envelope or, on the other hand, a more limited work envelope might be sufficient.
In the realm of articulated boom lifts and other similar structures, a significantly large work envelope, although possibly desirable in view of the number and variety of boom positions that might be attainable, might sacrifice lift stability as a result. For example, there might be several rearward positions in a large work envelope that could invite backward instability. For this reason, many previous efforts have sought to decrease the available work envelope in order to eliminate positions of backward or forward instability. However, as will be discussed herebelow, most such efforts have involved specific structures and components that are complex in nature and do not easily lend themselves to facilitating customization of the apparatus or lift in question for particular intended uses.
Certain types of conventional boom lifts, such as the JLG 600A boom lift manufactured by JLG Industries of McConnellsburg, Pa., are of an xe2x80x9carticulatedxe2x80x9d nature, and include the following basic components: tower boom, upright, upper boom and related hydraulic cylinders. Typically, provisions are made to permit the upright to be leveled by way of cylinders, in relation to the horizontal. Similar provisions can be provided to level the work platform in continuous manner. In several conventional approaches, there is a master-slave cylinder relationship between the work platform and the upright that permit both items to remain level, as in commonly assigned U.S. Pat. No. 4,775,029 to MacDonald et al, which is hereby incorporated by reference as if set forth in its entirety herein.
Other conventional articulated boom lifts, on the other hand, involve the use of multi-segmented tower booms. Also, several conventional lifts utilize parallelogram bars or xe2x80x9cpseudo-parallelogramxe2x80x9d bars in tower booms or tower boom segments.
Some examples of lifts that involve a purely independent relationship between a tower boom and upper boom, or between two segments of a multi-segmented tower boom, are discussed herebelow.
In the aforementioned MacDonald patent and in many other known arrangements, the upper boom moves completely independently of the tower boom. Typically, one or more hydraulic cylinders (i.e., lift cylinders) might extend between the upright and the upper boom for the independent purpose of controlling the movement of the upper boom, while one or more other hydraulic cylinders (leveling cylinders) might extend between the tower boom and the upright for the purpose ofkeeping the upright level. Of course, one or more hydraulic cylinders will preferably be provided to raise the tower boom itself.
Advantages have been enjoyed in conjunction with structures such as those just described, in comparison with previously known arrangements. For instance, the aforementioned patent to MacDonald et al. lends itself readily to the incorporation of a telescoping tower boom, which itself provides the advantage of selective extension of the tower boom to achieve significant raising of the upper boom without the need to resort to a fixed-length tower boom that might have an undesirably large stowed length. The raising or lowering of the tower boom in the MacDonald patent is always hydraulically in tandem with the upright member interconnecting the lower and upper boom, thereby maintaining the upright member in a level or plumb position. In a generally similar manner, the raising or lowering of the upper boom is accomplished in coordination with the orienting of the operator""s platform so as to maintain the latter at a level position regardless of the angle of elevation of the upper boom. All of these features are accomplished while at the same time providing a boom lift having a relatively low stowed height and stowed length for convenience of transportation, and having relatively few moving parts and pivot points for maintaining the operator""s platform in a level position. Other details relating to structural and operational aspects of the structures just described may be found in the aforementioned patent to MacDonald et al.
The Snorkel company of St. Joseph, Mo., has produced a series of lifts, namely the xe2x80x9cUNO 4xc3x974 Seriesxe2x80x9d, in which two tower boom segments are completely independent with respect to one another. Thus, there are completely separate and independent cylinders that separately actuate each of the two tower segments. No arrangement appears to be provided for automatically limiting the range of movement of the tower segments. The inherent disadvantage of such an arrangement is that the working envelope is so broad as to increase the number of potential positions of instability. U.S. Pat. No. 4,944,364 to Blasko also appears to disclose an arrangement that involves independent motion of the upper boom and tower (or lower) boom with respect to one another. Particularly, two cylinders are used in series to increase the range of motion of the lower boom, and a linkage in between them is provided to maintain the necessary mechanical advantage.
U.S. Pat. No. 4,643,273 to Stokoe appears to disclose an arrangement in which an upper boom moves independently with respect to a lower boom, yet the independent motion of the upper boom is restricted. In the Stokoe patent, a cylinder appears to extend between a lower boom and an upper boom and an intermediate linkage appears to be necessary. The cylinder is pinned not on the lower boom itself or any portion thereof, but on a linkage that is separate from a hinge. Therefore, this would appear to be analogous to the known concept of pinning an upper lift cylinder on a component that is itself an intermediary between upper and lower boom structures, and would thus not appear to represent a significant departure from that concept. The result of the Stokoe arrangement appears to be nothing more than increasing the range of angular motion between the two booms.
The Stokoe arrangement appears to disclose an independent relationship of the upper boom and tower boom with respect to one another, but this appears to be restricted by a xe2x80x9cstair-stepxe2x80x9d procedure that is used for raising the work platform. Particularly, it appears that the upper boom cannot be moved until the tower boom is raised. This discretely segmented method of raising the booms would appear to encompass several disadvantages, not the least of which are the inefficiency of movement, unreasonably limited ranges of movement, and possible discomfort and inconvenience for the operator on the work platform.
U.S. Pat. No. 3,894,056 to Ashworth appears to disclose an arrangement in which a cylinder, pinned on a lower boom, actuates without any other intermediary components that are directly attached to an upper boom, although it would appear that a rather complex arrangement is disclosed. Particularly, as best illustrated by FIG. 2 of that patent, a first cylinder, pinned on the lower boom, is connected to the upper boom via a rod. However, a second rod is also present, this being connected at another point on the lower boom. The result is merely to extend the range of angular motion between the two booms. Further linkages and rods are also disclosed which operate in an apparently complex manner in order to limit the positions of the booms and thus prevent the entire boom structure from assuming a potentially unstable configuration.
Generally, in the Ashworth device, independent movement of the upper and lower booms with respect to one another is afforded by separately actuable hydraulic cylinders. Since the complex system of stops and linkages appears to be geared to the very specific purpose of limiting the action of the separately actuable cylinders to maintain lift stability, it would appear that versatility in positioning might be sacrificed. Furthermore, the structure disclosed in the Ashworth patent, since it involves fixed linkages between the tower boom and the upper boom, would appear to preclude the use of a telescoping tower boom, which itself has its own attendant advantages as discussed herein.
The disclosure now turns to a discussion of previous efforts that involve a strictly dependent relationship between an upper boom and a lower boom, or between two segments of a multi-segmented tower boom.
U.S. Pat. No. 4,953,666 to Ridings appears to disclose an elevating apparatus for raising and lowering a work station between a downwardly declining, compact retracted position and an upwardly inclining extended limit position. The work station is connected to a mobile support base by parallelogram first and second boom assemblies which are operatively interconnected by a boom assembly coupler and rigid compression link. Raising or lowering the first boom assembly by a hydraulic lift cylinder arrangement causes the second boom assembly to move correspondingly such that the work station moves vertically, unaccompanied by any substantial horizontal motion, and is maintained in a level attitude throughout the range of motion of the apparatus via the action of the parallelogram arms.
Some disadvantages and shortcomings have been noted with the Ridings device. Primarily, the two booms are completely dependent on one another for their movement, thus imparting to the lift a potentially limited range of composite boom positions. The options available to the operator are thus quite limited. For example, there is essentially no provision for gaining additional xe2x80x9coutreachxe2x80x9d, or supplemental horizontal positioning for given vertical positions.
Genie Industries of Redmond, Wash., has developed a xe2x80x9cZ-45/22xe2x80x9d lift that involves a two-segment tower boom, with parallelogram structures used for each of the segments. In similar manner to the Ridings device, motion between the two tower boom segments is completely interdependent. The link between the two tower boom segments is apparently similar to that of the Ridings device, as well.
In the aforementioned Genie device, a hydraulic cylinder is also added between the two tower boom segments, but this appears to be nothing more than a lift cylinder that, because of the interdependency between the two tower segments, provides all of the lifting action for the two tower segments (even for movement of the lower tower segment with respect to the chassis). Because of the parallelogram structure of the tower boom segments, neither segment can readily lend itself to the incorporation of a telescoping tower boom segment.
Finally, the Calavar Corporation of Waco, Tex., has produced an articulated telescopic boom lift, namely the Condor 86A, which involves a mechanical four-bar linkage for displacing the upright. The platform is not apparently leveled relative to the upright, but is apparently leveled electronically by way of tilt sensors in the platform area of the lift. No leveling relationship is thus maintained between the upright and the horizontal.
Apparently, the upright changes its vertical orientation as the tower boom is raised from its stowed position to its fully elevated position. Apparently, the placement of the four-bar linkage pins serves to carry out this angular change of the upright, possibly by rendering the linkage bars slightly out of parallel with respect to one another (when viewed along a vertical plane). The upper boom lift cylinder is pinned to the upright, so the upper boom changes angle as the tower boom is raised.
Some disadvantages have been noted, however, with respect to this Condor design. For one, the four-bar linkage prevents the use of a telescopic tower boom, thus limiting the height of the upper boom and adding to horizontal outreach, thus increasing the potential for forward instability. Further, as mentioned above, the constantly changing upright angle precludes the use of hydraulic leveling of the platform, meaning that the aforementioned complicated arrangement of tilt sensors is required. Additionally, the upright is inclined when the boom is in the stowed position, thus adding to stowed length and to the degree of tailswing. Because of the increased degree of tailswing, there is also the potential for increased backward instability.
Another disadvantage with the Condor device may be found in that the four-bar linkage places limitations on the location of the upper lift cylinder. Particularly, the positioning of the lower four-bar linkage appears to necessitate placement of the upper boom beside the lower boom, rather than in a xe2x80x9cboom-over-boomxe2x80x9d arrangement, in which the center lines of the booms essentially lie in the same vertical plane to permit one of the booms to nest within the other with the booms in a stowed position. The disadvantage of such an arrangement is that the composite boom structure will have a greater width than might be desired, thus adding complexity to packaging and transport, and the offset center lines of the booms will result in a lateral moment, which might lead to unwanted deflections in the machine.
In view of the foregoing, a need has also thus been recognized in conjunction with the provision of a lift arrangement in which a degree of versatility and flexibility is offered with respect to both maintaining stability of the lift and affording a desired range of motion.
In accordance with a presently preferred embodiment of the present invention, the upper lift cylinder has essentially become multi-functioned, in that it is used as a link to tie the motion of the tower boom to the upper boom as well as being used as an actuator for upper boom positioning. The booms are thus tied together mechanically so when the tower boom is raised, the upper boom is also raised due to the geometry of the upper boom lift cylinder attachment. Furthermore, this arrangement advantageously permits the use of a telescoping tower boom (if desired) as well as a master-slave connection between an upright and a work platform.
Generally, at least one presently preferred embodiment of the present invention broadly contemplates load-bearing apparatus comprising: a first arm portion; a second arm portion; and at least one element for: selectively imparting a predetermined dependent relationship between the first and second arm portions; and selectively imparting a predetermined independent relationship between the first and second arm portions.
Further, at least one presently preferred embodiment of the present invention broadly contemplates a method of making load-bearing apparatus, the method comprising the steps of: providing a first arm portion; providing a second arm portion; and providing at least one element for: selectively imparting a predetermined dependent relationship between the first and second arm portions; and selectively imparting a predetermined independent relationship between the first and second arm portions.